The discussion of the principle in question points to the concern that wars take place at all only due to the fact that there exists no court that has rightful force with regards to disputes between states or, in other words, that there is a state of nature between them. Since there is no ground for determining the right in the dispute it follows that neither enemy can be declared unjust in themselves, states Kant. It is rather only by means of the outcome that a verdict is delivered. Since there exists no prior ground of right between the states there is no basis for declaring that a given enemy deserves annihilation. In fact if one state declares this against another then the second has an equal right to declare the same in return which would produce the perpetual peace "of the graveyard of the human race" (Ak. 8: 347).
So it is against this general background of argument that Kant's prohibitions on certain strategies is to be understood. The strategies in question can only be grounded on a relation to the enemy that treats that enemy as something deserving to be classed in a manner quite different from oneself since the tactics and strategies in question deny common humanity. Thus the general argument turns, as we have discovered to be the case with other preliminary articles, on reference to the formula of humanity. The second point of the general argument is that the strategies in question have no means of being terminated once begun but will create a perpetual state of war.
There are a number of questions that arise from considering the argument for the principle in question here. Firstly, the assertion of the "state of nature" between states is one that Kant returns to, as we shall see in future postings, on a number of occasions. It is however denied by some contemporary political theorists who assert that international law has taken us beyond the "state of nature" picture. This is the view of Habermas for example and the argument between Kant and Habermas on this point will have to be returned to subsequently.
Secondly, the argument that there is no such thing as an "unjust enemy" appears to be one that is difficult to sustain in light of the 20th century experience of Nazism, a regime that appears to incarnate inhumanity. It is however still worth appealing to some version of Kant's argument even here as is done by those who object to the fire-bombing of Dresden. However, even if mitigated by examples like this, it still appears less obvious now than it did to Kant, that there are no grounds for declaring some enemies to be in themselves intrinsically "unjust". This evidently points again to the question of the status of "international law".
Thirdly, Kant's general concern with preventing perpetual war is one that has returned to haunt subsequent theory of relations between states. The suggestion of such a condition having been reached is forcefully presented in George Orwell's 1984 on the one hand and in the development of the Marxist theory of the permanent arms economy on the other (the latter part of the theory of imperialism). The appeal during the Cold War to the theory of mutually assured destruction (MAD) also involved a suggestion converse to that animating Kant's discussion since according to this the best way of preventing war was to constantly threaten the arrival of the perpetual peace of the graveyard.
Finally, returning to Kant's specific examples, we can see in them an appeal for guidelines in the event of war as to what constitutes acceptable conduct, an appeal that relates Kant to the earlier Just War tradition. Ruling out use of assassins or poisoners is clearly intended to prevent the systematic use of deceit being adopted and in the remarks Kant uses a similar justification against the use of spies since these involve use of others dishonesty. The appeal here is clearly connected to a principle of publicity being assumed though not at this point in Perpetual Peace directly argued for. Incitement to treason and breach of surrender both involve breach of trust by contrast and little is added by way of specific discussion of the point of taking this seriously.